The present invention relates to a gearbox for a vehicle, such as an agricultural vehicle. The gearbox is of the type known as a trans-axle which incorporates a differential and half-shafts of an axle, as well as a change speed gear.
Many agricultural tractors are constructed without a complete chassis or frame and the gearbox is not merely part of the transmission; it is also a structural item performing part of the function of a chassis. In such constructions, the gearbox is a strongly built, expensive item and a range of vehicles of different sizes and powers requires a corresponding range of gearboxes. Manufacturing costs are therefore high.
A gearbox described in our U.S. patent application, Ser. No. 419,091, filed Sept. 16, 1982, is a transverse gearbox in which the rotating components are mounted essentially on two parallel shaft lines, one of which is also the line of the two rear axle half-shafts. The components of the gearbox are contained within a housing formed of upper and lower parts with a parting plane which contains the aforesaid two shaft lines. The components can thus readily be assembled into the bottom casing part, the top being thereafter fitted. Servicing, as well as manufacture, is simplified. The casing is preferably of relatively light shell form, the gearbox being a non-structural part mounted in the framed vehicle.
The transverse gearbox is very compact in the longitudinal direction of the vehicle which has advantages in relation to the layout of the vehicle as a whole. However, the gearbox is necessarily of substantial transverse width, especially having regard to the incorporation not only of the change speed gear, but of a range gear, possibly the creep gear, differential, PTO drive and even a mechanical front wheel drive. It would appear to be impossible to fit such a transverse gearbox into narrower agricultural vehicles, such a vineyard or orchard vehicle having an overall width of 1 m or 1.5 m. Although the prior proposal includes mechanical front wheel drive, there is no longitudinal differential. This term is used to denote a differential which divides the power longitudinally, i.e. between the front and rear axles. The differential dividing power between the two half-shafts may correspondingly be referred to as a transverse differential.
The prior proposal furthermore employs a six-speed, change-speed gearbox and a three-speed range gear giving eighteen normal gears. Such a range of gears will typically give road speeds from 1.5 km/h up to 30 km/h, assuming that the gears are sufficiently closely spaced. 30 km/h is a very low speed for traveling on the road and it is desirable to achieve a top speed more like 40 km/h. This requires even more gears and it is difficult to achieve this in a transverse gearbox, as described in the aforesaid prior application.